Reinforced polystyrene and its copolymers

ABSTRACT

Polystyrene and copolymers thereof can be reinforced by glass fibers having a coating of silane coupling agent and a thermosetting polymer such as epoxy, phenolic, polyester, polyacrylate and melamine, to provide superior thermoplastic injection molding compositions.

United States Patent l 72] inventor Robert C. l-lartlein Midland, Mich. [21 Appl. No. 757,749 [22] Filed Sept. 5, 1968 [45] Patented Nov. 9, 1971 [73] Assignee Dow Corning Corporation Midland, Mich.

[ 54] REINFORCED POLYSTYRENE AND ITS COPOLYMERS 10 Claims, No Drawings [52] U.S. C1 117/4. 1.17/72,117/76 T.117/126 GS [51 Int. Cl. C03c 25/02 [50] Field oiSeareh 117/4, 126 GS, 72. 76 T; 161/93 [56] References Cited UNITED STATES PATENTS 2,877,501 3/1959 Brad! 117/4 Marzocchi et a1.

Primary Examiner-Alfred L. Leavitt Assismn! Examiner-M. F. Esposito Anorneys- Robert F. Fleming, Jr., Laurence R Hobey and Harry D. Dingman ABSTRACT: Polystyrene and copolymers thereofcan be reinforced by glass fibers having a coating ofsilane coupling agent and a thermosetting polymer such as epoxy. phenolic. polyester, polyacrylate and melamine, to provide superior thermoplastic injection molding compositions.

REINFORCED POLYSTYRENE AND ITS COPOLYMERS SPECIFICATION This invention relates to a method for making improved thermoplastic compositions by the use of thermosetting resins as sizing for glass fibers. In particular, this invention relates to a novel method for producing reinforced thermoplastic molding compounds of polystyrene and its copolymers and mixtures of copolymers. Additionally, the invention relates to composite articles of the described resins and glass fibers.

It has been sought by workers in the organic polymer field to enhance the physical properties and strengthen certain inexpensive and commercially available thermoplastics such as polystyrene by employing glass fibers. Since polystyrene monomers consist of -CH,C H CI-I 0 the polymer is generally nonreactive. This characteristic of polystyrene poses a coupling problem in that the thermoplastic fails to adhere to surfaces of glass fibers. As a result of the poor bonding between treated glass fibers and the thennoplastic material, the contribution of strength is less than could otherwise be achieved. The invention provides improved bonding by the proper selection of a combination of the defined thermosetting resins and silane coupling agents as a precoating for the glass fibers.

A second problem involves uniformity of distribution of the glass fibers throughout the molded article. Of the several ways to mix glass and thermoplastic resins one of the most economical is to dry blend the glass fibers and the resin. However, unless the dry blend is homogeneous, a nonuniform distribution of glass is obtained when the blend is fed to the melt cylinder and from there to the mold. This results in lower strength articles. The process of this invention has solved this problem because the individual fibers stay in bundles during chopping and blending and thus do not fonn fuzz and segregate from the particles of styrene. However, the fibers are not so tightly bound that they will not separate during extrusion of the thermoplastic-glass mixture into the mold. Thus, a uniform mix of individual fibers is obtained in the final product. It is important to note that this uniform blend can be obtained with polystyrene pellets. This eliminates the necessity of grinding the resin to a fine powder and results in considerable savings.

A third problem has to do with the integrity of the glass fiber during the molding and mixing operation. Unless the fibers are adequately protected from abrasion they will disintegrate and loose their reinforcing ability. The coating employed herein gives excellent protection to the glass.

It is an object of this invention to produce a method for improving the contribution of strength of treated glass fibers in polystyrene and copolymers thereof. It is another object of this invention to produce a novel method of reinforcing thermoplastics to obtain optimum strength and reinforcement. It is a further object of this invention to provide a novel composite blend that can be readily molded into a thermoplastic article of marked rigidity and increased stability over that obtained using untreated materials. It is a further object to provide a novel treated glass roving with improved handling properties. Other objects and advantages will be apparent from the following description.

According to the invention, there is provided a method of I making a thermoplastic molding compound which comprises 1. coating glass fibers with a A. an organosilane having attached to the silicon through a silicon-carbon bond at least one functional group reactive with a thermosetting resin selected from the group consisting of aromatic epoxy, phenolic, polyester, polyacrylate and melamine resins, at a temperature below the decomposition temperature of the resin, (A) having at least two hydrolyzable groups attached to the silicon or hydrolysis products of (A B. a thermosetting resin selected from the group consisting of aromatic epoxy, phenolic, polyester, polyacrylate and melamine resins, (B) being present in amounts such that the weight pickup of said thermosetting resin on the glass is from 0.25 percent to 15 percent by weight based on the weight of the glass,

2. bringing the thennosetting resin to such a state that the coated fibers can be chopped without sticking to the chopper,

3. chopping said fibers, and thereafter 4. curing the resin coating and 5. blending sufficient polystyrene or copolymers thereof with said treated glass fibers whereby a blend of glass fibers and polystyrene is obtained having the bulk density of approximately the bulk density of polystyrene.

The term polystyrene" as used herein includes polystyrene per se and copolymers of styrene and other vinylic monomers containing at least 50 mol percent. 7

In accordance with the best mode of practicing of this invention, glass roving is passed through a bath containing the above-described organosilane. After being dried it is then passed through a second bath containing above-described thermosetting resin which has been precatalyzed. The roving so treated is then dried at a low-temperature to reach a tacky state just prior to and during the chopping operation. By this method frizzing is prevented. Thereafter, the chopped materials are fully cured and mixed with the polystyrene.

It is, of course, understood that a one-bath system can be employed in that a solution of the silane, or its hydrolyzate and thermosetting resin can be applied in a single operation. Thus, the silane coupling agent may be mixed with the thermosetting resin, cured to a tacky state, chopped, fully cured and mixed with the polystyrene. Hence, the treatment of glass fibers according to this invention produces a composite whereinthe glass-thermoset interface is substantially united chemically and the thermoset-thermoplastic interface is substantially bonded nonchemically.

In order to enhance the handling and chopping properties of roving, glass fiber manufacturers presently add certain silanes to their glass sizings. Because of film hardness, choppability is generally impaired. The method of this invention produces glass roving that is easy to handle and chop due to the slight adhesion achieved by maintaining a tacky state prior to the chopping operation. Thus, it is extremely important that the glass be chopped while the thermosetting resin is in its uncured state since the coating is soft and flexible and no balling or frizzing of the fibers results. In addition, markedly improved processing characteristics may be obtained by this in vention. Because the bulk density of the chopped fibers approximates that of the thermoplastic material, dry blends thereof can be readily molded to yield a uniform dispersion of coated glass fibers in a thermoplastic matrix.

Any commercial type of glass fiber can be used in this invention. The term glass fibers indicates glass rovings, yarns, milled fibers, strands, bundles or fabric used to give reinforcement to the thermoplastic material. Generally, as the length to diameter of the glass fiber increases the reinforcing effect becomes more pronounced. Thus, chopped glass fibers having about one-fourth inch length are generally preferable.

Silane or siloxane coupling agents serve to bond glass to an organic thermosetting polymer. In effect, a strong bonding relationship is formed between the hydrophilic end of the coupling agent with the glass substrate and a likewise strong bonding relationship is formed at the other end of the coupling agent with the thermosetting substance. Thus, the coupling agent functions as a molecular bridge which serves to tie the organic polymer coating with the hydroxyl-conta'ining glass substrate.

The coupling agents used herein are well known materials and have been described in various U.S. Pat. Nos. and publications such as U.S. Pat. Nos. 3,306,800, 3,249,464, 3,079,361 and 2,946,701; and articles by E. P. Plueddemann et al. in Modern Plastics, Vol. 39, pg. 135, Aug. 1962, and Vol. 40, pg. 133, June 1963, which disclosures are incorporated herein by reference.

For the purpose of this invention the coupling agent can be any silane having a functional group attached to the silicon through a silicon-carbon bond and having two or three hydrolyzable groups attached to the silicon atom or reactants forming the resin contains an aromatic ring. These hydrolyzates of such silanes. Thus, the coupling agent can be a materials are commercially available. Low molecular weight silane,asilanolorasiloxane. epoxy resins derived from bisphenol A and epiehlorohydrin As used in this specification hydrolyzable group," is answer well to the present invention. The polymers can be defined as those silicon-bonded radicals which are replaced by 5 Cured with a Catalyst Such as 'y amines or they can be water at substantially room temperature to form a silanol radici'ossiihked with a Variety of hardeheisq in addition the epoxy cal, i.e. Si-OH. Such groups are well known to the art, i'esihs y be modified with Phehoiic acrylic representative examples being alkoxy groups, such as methoxsoihe other thff'i'mosenihg in Short, y aromatic PQ y, ethoxy, allyloxy, gmethoxyethoxy, and isopropoxy; acyloxy resins cured with any of the common catalyst and/or crosslmgroups such as acetate, propionate, butyrate; halogen groups kers is operative herein t such as chbride, bromide and iodide; ketoxime such as Both the base catalyzed or resol and the acid catalyzed or novolak phenolic resins (phenolaldehyde) can be satisfactorily used in the present invention. in addition, the phenolic H5O resins may be modified with epoxy or other thermosetting C=No i5 resins without departing from the present invention. Hi0 The term polyester is used herein to refer to polymers made 'fl l y from dior polyfunctional alcohols and dior polyfunctional (Ci-[ 0 C N() d h isocyanaze group, acids. These include polyesters containing aliphatic C=C.

Thus, the polyester can be based on saturated alcohols and unsaturated acids such as maleic or fumaric acids or anhydrides or unsaturated alcohols such as allyl alcohol. The latter would include allyl phthalates. The term also includes the so-callcd alkyl resins which are reaction products of polyhydric alcohols and dibasic acids and which do not include C=C aliphatic unsaturation. If desired, the polyesters can be modified by ineluding therein vinylic monomers such as styrene or they can be modified with drying oil acids.

The polyacrylic esters used herein are polymers of the esters of acrylic and methacrylic acids. These resins are rendered thermosetting by including polyfunctional monomers in the copolymer such as hydroxypropylmethacrylate, diacrylyl,

in selecting a coupling agent, particular attention must be paid to the organic portion of said agent. It should be realized that the nature of the linkage between the siliconorganic functional portion of the coupling agent is immaterial so long as it is stable; that is, so long as it is free of hydrolyzable linkages such as silicon-oxygen, silicon-nitrogen, etc., which render any group containing them unstable. in short, the silicon of the coupling agent must be linked to the reactive organic portion of the coupling agent through silicon-carbon linkage. Again, the linking group can contain other atoms such as O, S, N, etc., so long as they are not attached directly to a silicon atom. Thus, the organic functional portion can be, for example, of

i group. cqnslstmg lfzepoxy lmmo Vmyl glycolate, glycidoxypropyl acrylate and other monomers well vinylene, vlnylldene, aliphatic halogen, lsocyanato, mercapto, known in the am hydroxyl, carbonyl and carboxyl. The melamine-formaldehyde resins can also be used as the one cardinal f of the that the thermosetting coating. These materials are well-known and glass fibers coated with the appropriate coupling agent are any type melamine formaldehyde resin can he used chemically receptive to certain thermosetting resins in that a Aside from providing a Surface to Which the thermoplastic substantial bonding is obtained between the thermoset and the n adhere one principal f ti f the thermosetting resin Coated fibers Presumably, this is due to an interaction 40 is to protect the glass fiber integrity during fabricating and between the thermosetting resin and the Organic Portion of processing. Manifestly, when the thermosetting resin is primed Said agent however, this ihvehiioh is in no way restricted to to the glass surface it gives increased rigidity to the glass fibers such an expiahaiiohih event it is generally that best in that there is a minimum of fiber rupture or glass filament bonding is obtained using those organosilicon compounds in damage du i ub e t milling or extrusion, Thus, when which the organic functional group is reactiv ith a un the cured material is blended with a thermoplastic resin the tional group in the thermosetting resin, Thus, by way of examglass fiber integrity remains intact, in that there is a minimum pie, the following table matches the thermosetting resin with of breakage or damage, and there is no substantial removal of the best known type of coupling agent for the resin. the thermosets protective coating.

RESIN WITH APPROPRIATE COUPLING AGENT Organic function of coupling Thermosetting resins agent Example of coupling agent Epoxy 1,2 epoxy amino H C'(|3CHiO(OH2)aSi(OOH;)a

Phenolic novolack resol Amino 1,2 epoxy N 1H(CH2)2NH(CH2)3S1(OCH3)3 Polyester Vinylic 1,2 epoxy vinylene- CH= C(UHa)CO0(CH2)3Si (00113); Polyacrylato. Vinyl 1,2 epoxy CH2=OHSi(OOOOH )q Melamine-.. Chloroalkyl. 1, 2 epoxy C1(CHz)3Si(OOH3)5 The organosilicon coupling agent may be applied by various The thermoplastic that can be reinforced by this invention is conventional means: roller, spray or flow methods or by impolystyrene and its copolymers. Polystyrene is formed from mersing the glass strands in a bath of treating composition. the addition polymerization of styrene. In order to be an effec- The treated fibers can be allowed to air dry or drying can be tive thermoplastic material reinforced to achieve optimum accelerated by heat. strength and excellent molding and extrusion properties, the

It will be appreciated that there are a number of therstyrene concentration in the copolymer should be at least 50 mosetting resins which are appropriately suited for the coating mol percent and preferably from to 80 mol percent. Any process l of this invention. Although outstanding improvecopolymer of styrene and other vinylic monomers can be used ment is obtained by employing aromatic epoxy or phenolic herein. The other monomers include alpha-methylstyrene. resins with the proper coupling agent. other thermosetting 70 acrylonitrile, methylmethacrylate, ethylacrylate, vinyltoluene resins can also afford very satisfactory results. Suitable and butadiene. polyme nclude polyqcrylute. polyester (including dialin orderto uttuin appreciable reinforccn1cnt,utlcust l0 perlylesters of polybusic acids), and melamine materials in addi- Cent EIHSS fiber y ig Should be P n the blcfld of tion to phenolic and epoxy resins. fibers and thermoplastic and preferably at least 25 percent.

Aromatic epoxy resins are those in which at least one of the ug these Proportions are not Criiicah of 200 g. acetone and L680 g. toluene into A typical composite concentration would be:

75 percent Thermopiasiic Glass fiber 24 percent Thermoset 0.9 percent Coupling ugeni 0.l percent EXAMPLE l Using a two bath system, glass strands were first dipped into an aqueous solution of 0.5 percent -y-glycidoxypropyltrimethoxysilane with l percent acetic acid and dried. The treated strands were passed through a second bath consisting which 60 g. 'epoxy novalac (DEN 431, Dow Chemical Co.) and 60 g. nadic methyl anhydride with 0.6 g. benzyldimethylamine were dissolved The amount of the coating applied did not exceed l percent by weight of the glass. When the strands were in a tacky or sticky state they were chopped and then cured {or 2 hours at 350 F For in ection molding, 35 percent by weight of glass coated with the cured material was dry blended with 65 percent by weight of a commercial styreneacrylonitrile copolymer. in testing samples thus produced, the tensile strength was l2.750 psi and the flexural strength was 24,600 p.s.i.

EXAMPLE 2 EXAMPLE 1 A commercial fiber glass which was pretreated at the bushmg with a hydrolyzate gamma-glycidoxypropyltrimethoxysilane. and was employed as in example 1. The resulting coated glass fibers in the amount of 35 percent by weight was dry blended with 65 percent commercial styrene-acrylonitrile copolymer. A second sample was also made using polystyrene instead of the named copolymer The flexural strength for the first same was 23 850 p s I and 2| .9 p.s.i. for the second.

EXAMPLE4 Using a two-bath system glass strands were first treated with an aqueous solution of g gamma-glycidoxypropyltrimethoxysilane and U l percent acetic acid and subsequently dried The coated strands were then passed through a second bath consisting of l5 g Shell Chemicals Epon 828, an epichlorohydrinbisphenol A type epoxy resin, with 3] g. curing agent. an aromatic amine. in 200 g. acetone and 2,] 13g. toluene The amount of coating on the glass did not exceed 15 percent by weight of the glass When the strands were still in a tacky or sticky state they were chopped into one-fourth inch lengths and cured tor 4 minutes at 300 F. For injection molding 35 percent i weight cured material was dry blended with 65 percent polystyrene Samples from this composition produced a material that had a tensile strength of 13,250 p.s.i and a flexural strength of l9.600 p.s.i

EXAMPLE 5 G ass strands are passed through a coupling bath having 05 percent y-glyciodoxypropyltrimethoxysilane and 0.l percent acetic acid and dried. The strands were then passed through a thermosetting bath made up of [00 g. epoxy novalac (DEN 43], Dow Chemical Co. i. 100 g. nadic methyl anhydride, l g. bcnzyl dimethylaminc. in 200 g. acetone and 2,099 g. toluene.

The amount of coating applied did not exceed l5 percent by weight of glass. When the treated strands were in atacky or sticky state theywere chopped and then the coating was further-cured for min. at 400 F. For;injection molding 35 percent by weight of the cured, chopped material was dry blended with percent copolymer of styrene acrylonitrile Samples from this examplehad a tensile strength of 20,740

psi and a flexural strength ot'24,900 p.s.i.

EXAMPLE 6 Glass strands were passed through a bath of coupling agent having 0 5 percent glyciodoxypropyltrimethoxysilane with 0.l percent acetic acid and subsequently dried.. The strands were then passed through a bath of 5 percent phenolic resin (ELL 3,085. Union Carbide )in isopropyl alcohol After being partly cured and. while still tacky, the strands werechopped. The treated fibers were then further cured for 30 minutes-at 350 F. For molding compositions, 20 percent' by weight of the cured and choppedmaterial was dry blended with 80 percent polystyrenewThe samples produced by this example gave a tensile strength of 9,380 p.s.i.

EXAMPLE 7 Glass strands were passed through 0.5 percent gammaglyciodoXypropyltrimethoxysilane and 0.l percentacetic acid in water and then dried. Thereafter. the strands were passed through a bath made up of 7.5 percent ofa commercial ther mosetting methylmethacrylate resin containing glycidoxypropylacrylate in toluene. The amount of these coatings did not exceed.l5 percent by weight of the glass -When the treated strands were in a tacky or sticky state. they were chopped and then the coated fibers were further cured for3U minutes at 50 F For injection molding, percent by weight of polystyrene was blended with 25 percent glass fibers'as above treated resulting in a material having a tensile strength of 7,280 psi In a like manner 75 percent by weight of styrene-acrylonitrile was blended with 25 percent glass fibers as treated above. yielding a tensile strength of9b l 0 p.s.i

That which is claimedis; I

l A glass-reinforced thermoplastic composite consisting es sentially of v l a thermoplastic resin selected from the group consisting of polystyrene and copolymers of polystyrene containing at least 50 mole percent polystyrene.- and blended therein 2 glass fibers coated with (a) anorganosilicon coupling agent having an organofunctional substituent; selected from the group consisting of epoxyuamino. imlno. vinyl. vinylene. vinylidene. aliphatic halogen. isotyanato mer capto. carbonyl, carboxyl and hydroxyl radicals said radical being attached to the silicon atom through a silicon-carbon linkage. and (b) a thermosetting resin selected from the group :consisting of. aromatic epoxy resins. polyesters, polyacrylates and melamines; said resin being reactive with the organofunctional substituent of the coupling agent (a) at a temperature below the decom position temperature of the thermosetting resin 2 The composite of claim 1 containing at least lll weight percent ot glass fibersi 3 An article in accordance with claim 1 in which the coupling agent la) is CH =CHCH O(CH J -,Si ()(H i. and the thermosetting resin (b) is an aromatic epoxy and the ther moplastic resin is polystyrene 4 An article in accordance with claim I in which the ther mosetting resin (b) is phenolic.

5 An article in accordance with claim I in which the coupling agent 1 a I is H N(CH NH(CH SI( OCH,

6. A method of making a thermoplastic molding compound which comprises l. coating glass fibers with a. an organosilane having attached to the silicon through a silicon-carbon bond at least one functional group selected from the group consisting of epoxy, amino,

imino, vinyl, vinylene, vinylidine, aliphatic halogen, chopper,

isocyanato, mercapto, carbonyl, carboxyl, and hydrox- 3. chopping said fibers, and thereafter yl radicals, said organosilanes having at least two 4. curing the resin coating; and

hydwlyzable groups attached to silicon y y- 5. blending sufficient polystyrene or copolymers thereof Sis Products ofsaid Organosilane 5 with said treated glass fibers whereby a blend of glass b. a thermosetting resin selected from the group consistfibers and polystyrcne is obtained having a bulk density g of aromatic f p y Phenolic Polyester p y f approximating the bulk density of the polystyrene.

late and melamme' said thermosemng min bemg 7. The method of claim 6 wherein 5 is a copolymer of present in amounts such that the weight pickup of said Styrene a acrylonitrih thermosempg resin on the glass from to f' lo 8. The method of claim 6 wherein 5 is polystyrene.

cent by we.lght blsed 9 the E y the & sad 9. The method of claim 6 wherein process 1 is accomplished thermosetting res n being reactive with the functional y concurrently coating and on a glass Surface group of organosflane (a) at a temperature below the 10. The method of claim 6 wherein the thermosetting resin coated fibers can be chopped without sticking to the 

2. bringing the thermosetting resin to such a state that the coated fibers can be chopped without sticking to the chopper,
 2. glass fibers coated with (a) an organosilicon coupling agent having an organo-functional substituent selected from the group consisting of epoxy, amino, imino, vinyl, vinylene, vinylidene, aliphatic halogen, isocyanato, mercapto, carbonyl, carboxyl and hydroxyl radicals; said radical being attached to the silicon atom through a silicon-carbon linkage, and (b) a thermosetting resin selected from the group consisting of aromatic epoxy resins, polyesters, polyacrylates and melamines, said resin being reactive with the organo-functional substituent of the coupling agent (a) at a temperature below the decomposition temperature of the thermosetting resin.
 2. The composite of claim 1 containing at least 10 weight percent of glass fibers.
 3. An article in accordance with claim 1 in which the coupling agent (a) is CH2 CHCH2O(CH2)3Si(OCH)3 and the thermosetting resin (b) is an aromatic epoxy and the thermoplastic resin is Polystyrene.
 3. chopping said fibers, and thereafter
 4. curing the resin coating; and
 4. An article in accordance with claim 1 in which the thermosetting resin (b) is phenolic.
 5. An article in accordance with claim 1 in which the coupling agent (a) is H2N(CH2)2NH(CH2)3Si(OCH3)3.
 5. blending sufficient polystyrene or copolymers thereof with said treated glass fibers whereby a blend of glass fibers and polystyrene is obtained having a bulk density approximating the bulk density of the polystyrene.
 6. A method of making a thermoplastic molding compound which comprises
 7. The method of claim 6 wherein 5 is a copolymer of styrene and acrylonitrile.
 8. The method of claim 6 wherein 5 is polystyrene.
 9. The method of claim 6 wherein process 1 is accomplished by concurrently coating (a) and (b) on a glass surface.
 10. The method of claim 6 wherein the thermosetting resin (b) is an aromatic 1,2-epoxy resin. 